Method of suppressing a periodical pattern in an image

Abstract

A short-time Goertzel transform is applied to the image signal to transform it into a representation of the spatial frequency component corresponding to the periodic pattern. This representation is processed. Next the inverse of the transformation is computed and the result of the inverse transformation is removed from the image signal.

1. A periodical pattern suppression method wherein a spatial frequency component corresponding to a periodical pattern occurring in an image signal is suppressed, comprising the steps of:
 extracting, via a radiography processing computer, from said image signal the spatial frequency component corresponding to the periodical pattern included therein by applying a transformation to the image signal to transform it into a representation of the spatial frequency component; 
 processing, via the radiography processing computer, the representation of the spatial frequency component; 
 computing, via the radiography processing computer, the inverse of the transformation on the processed representation of the spatial frequency component; and 
 suppressing, via the radiography processing computer, the spatial frequency component occurring in the image signal by eliminating from said image signal the result of said inverse transformation, wherein said transformation is defined by a formula
   Γ( y ,ω)=∫ w ×( x−y )× s ( x )× e   iωx   dx    
 
 wherein s(x) is said image signal, ω represents a given frequency of the periodical pattern, and 
 wherein said processing comprises applying a non-linear high frequency attenuating filter to the representation of the spatial frequency component. 
 
     
     
       2. A method according to  claim 1 , wherein the high frequency attenuating filter is implemented with a median filter. 
     
     
       3. A method according to  claim 1 , where the high frequency attenuating filter is a 2-dimensional filter. 
     
     
       4. A method according to  claim 1 , wherein the high frequency attenuating filter is a 1-dimensional filter in the same direction as the spatial frequency component. 
     
     
       5. A method according to  claim 1 , wherein the high frequency attenuation filter is a 1-dimensional filter in the orthogonal direction to the spatial frequency component. 
     
     
       6. A method according to  claim 1 , wherein the high frequency attenuating filter is a sequence of high frequency attenuating filters including at least one of a 1-dimensional filter and a two-dimensional filter. 
     
     
       7. A method according to  claim 1 , wherein the filter is applied to the imaginary part of the complex representation. 
     
     
       8. A method according to  claim 1 , wherein the filter is applied to the real part of the complex representation. 
     
     
       9. A method according to  claim 1 , wherein the filter is applied to the magnitude of the complex representation. 
     
     
       10. A method according to  claim 1 , wherein the filter is applied to the phase of the complex representation. 
     
     
       11. A method according to  claim 1 , wherein the transformation is applied to a filtered version of the image signal. 
     
     
       12. A method according to  claim 11 , wherein the filtered version of the image signal does not contain the DC component. 
     
     
       13. A method according to  claim 11 , wherein the filtered version of the image signal only contains frequencies within a certain bandwidth of the frequency to be suppressed. 
     
     
       14. A method according to  claim 1 , wherein the spatial frequency components are removed which correspond to an image of anti-scatter gridlines in a radiographic image. 
     
     
       15. A non-transitory computer program product adapted to carry out the steps of  claim 1  when run on a computer. 
     
     
       16. A non-transitory computer readable carrier medium comprising computer executable program code adapted to carry out the steps of  claim 1 .